The present invention relates to a III-V Group compound semiconductor laser device, and a method of manufacturing the same.
A semiconductor laser device using an AlGaInP semiconductor material is being developed as a light-emitting device in a visible region since it can be lattice-matched to a GaAs substrate and has the largest direct transition bandgap among III-V Group compound semiconductors. This semiconductor laser device is used as a light-emitting device in the visible region since data can be recorded in higher density particularly when used as a light source for an optical disc or audio/video disc.
Since high reliability is now required in high output operations, many structures that realize such a characteristic are being proposed.
A method of manufacturing a conventional semiconductor laser is described below with reference to cross sectional views in FIGS. 6A–6C and FIGS. 7A–7C.
As shown in FIG. 6A, first, an n-type GaAs buffer layer 102, n-type AlGaInP clad layer 103, GaInP active layer 104, first p-type AlGaInP clad layer 105, GaInP etching stop layer 106, second p-type AlGaInP clad layer 107, p-type GaInP intermediate layer 108 and p-type GaAs contact layer 109 are laminated on an n-type GaAs substrate 101 in a first growth step.
Subsequently, as shown in FIG. 6B, three layers of the second p-type AlGaInP clad layer 107, p-type GaInP intermediate layer 108 and p-type GaAs contact layer 109 are etched so that etching is stopped at the GaInP etching stop layer 106 to form a ridge 120.
Subsequently, as shown in FIG. 6C, an n-type AlInP current block layer 110 is laminated in a second growth step. This current block layer 110 is constituted by a summit portion 110A laminated on the ridge 120 and side portions 110B formed on both sides of the ridge 120 on the etching stop layer 106.
Subsequently, as shown in FIG. 7A, a resist 115 is applied on both sides of the summit portion 110A of the n-type AlInP current block layer 110 laminated on the aforementioned ridge 120, and the summit portion 110A of the n-type AlInP current block layer 110 on the ridge 120 is etched by a lithography technique to remove the summit portion 110A.
Meanwhile, upon this etching, the summit portion 110A of the n-type AlInP current block layer 110 laminated on the ridge 120 and the side portions 110B of the n-type AlInP current block layer 110 deposited on both sides of the ridge 120 are brought into contact with one another as shown in FIG. 7A. Alternatively, there is a narrow gap between the summit portion 110A and the side portions 110B.
Therefore, upon the etching, the side portions 110B of the n-type AlInP current block layer 110 deposited on both sides of the ridge 120 are also etched, and hence wedge-shaped gaps 121 are formed between the side portions 110B and the ridge 120 as shown in FIG. 7B. Then, a p-type GaAs contact layer 111 is grown in a third growth as shown in FIG. 7C, and a p-type electrode 117 and an n-type electrode 118 are formed.
In the above conventional example, as shown in FIG. 7B, the side portions 110B of the n-type AlInP current block layer 110 positioned on both sides of the ridge 120 are etched. Therefore, wedge-shaped gaps 121 are formed between the ridge 120 and the side portions 110B, and a structure in which wedge portions 111A of the p-type GaAs contact layer 111 enter these gaps 121 is obtained as shown in FIG. 7C.
Since this p-type GaAs contact layer 111 has a smaller bandgap than that of the GaInP active layer 104, light oscillating in the GaInP active layer 104 is absorbed in the wedge portions 111A of the p-type GaAs contact layer 111 existing on the sides of the ridge 120. Therefore, an oscillation threshold current or an operation current increases, and differential quantum efficiency declines, thereby resulting in deterioration of laser characteristics such as lower reliability.